1. Field
The disclosed aspects relate to wireless devices and wireless communication networks, and more particularly, to apparatus and methods for determining an estimated geographical position of a wireless device corresponding to events associated with wireless devices on a wireless network, in particular determining an estimated geographical position from based on one or more location fixes having Quality of Service (QoS) adjusted so as to provide for fixes that are based at least partly on terrestrial wireless communication measurements.
2. Background
Many wireless communications devices, such as mobile phones, pagers, handheld computers, etc., have the ability to determine the location parameters associated with the geographical position of a wireless device on the surface of the earth. The location parameters may include the position and speed coordinates for the wireless device. The wireless device may include a geographical position location system in the form of hardware, software and/or firmware and other associated parameters. One exemplary wireless device geographical position location system receives and analyzes location parameters derived from the Global Positioning System (GPS), a radio-navigation system, developed and operated by the U.S. Defense Department, that includes a series of 24 constellation satellites orbiting the earth at a distance of approximately 20,000 kilometers. The GPS position location parameters permit wireless device processors to determine their respective three dimensional positions and velocities using very precise location parameters and timing signals received from the satellites.
Currently various modes of operation exist for determining location using satellites. For example, GPS, Galileo, GLONASS (GLObal NAvigation Satellite System) or other satellite-based systems may rely on a Mobile Station-Based (MS-Based) mode, a Mobile Station-Assisted (MS-Assisted) mode, a Standalone mode or any other feasible mode currently known or known in the future. The various modes offer different methods for determining location. For example, in MS-Based mode the wireless device obtains information related to the location of satellites from a network Location Determining Entity (PDE) and then performs the location determination calculation at the wireless communication device. The satellite location information is commonly referred to as Ephemeris data and Almanac data. Almanac data is course orbital parameters for all the satellites in the system and is considered valid for up to several months. Ephemeris data by comparison is very precise orbital and clock correction for each satellite and is considered valid for about 30 minutes. Thus, in MS-Based mode a wireless device may, but is not always required to, obtain the information from the PDE depending on the currentness of the satellite information.
In MS-Assisted mode the wireless device relies on the PDE to perform the location determination and, as such, is required to communicate with the PDE each time a location determination is performed. Therefore, by comparison, while MS-Based mode requires a wireless signal to communicate with the PDE for some of the location determinations, MS-Assisted mode requires a wireless signal to communicate with the PDE for all of the location determinations.
In contrast, in Standalone mode all the functions are carried out at the wireless device and, since no PDE satellite information is required, no wireless signal is required. However, Standalone mode requires that the wireless device receive signals from all four of the GPS satellites, while MS-Assisted mode only requires communication with one or two of the satellites to determine position. Thus, Standalone mode has a high failure rate when attempts are made indoors, while the MS-Assisted mode is typically the mode of preference when attempts are made indoors.
In current practice, the applicable location determination mode is defined by the application or is chosen at the initialization/start-up stage. Thus, the chosen mode applies to location determinations requests even if the mode may not be the best mode for all scenarios. Various conditions may exist throughout the executing duration of an application that are relevant to the effectiveness of the chosen mode. For example, MS-Assisted mode requires a wireless signal, such as a CDMA (Code Division Multiple Access) signal or GSM (Global System for Mobile) signal and, therefore, if the chosen mode is MS-Assisted, location determination will not occur if the wireless signal is not active. Other conditions that affect the performance of location determination modes are the current environment of the device, battery life, voice call state, data call state, the currentness of the PDE satellite information and the like.
In addition to relying on satellites to determine location, certain modes, such as MS-Assisted mode or the like, may take base station measurements to provide a terrestrial-based location determination. Terrestrial measurements and associated terrestrial-based location determination refers to any terrestrial-based measurements and terrestrial-based location determination that does not involve the use of satellite signals and measurements. Examples of terrestrial-based methods used to determine wireless device location include, but are not limited to, Advanced Forward Link Trilateration (AFLT), Enhanced Forward Link Trilateration (EFLT), Enhanced Observed Time Difference (EOTD), and the like. AFLT is the method generally associated with MS-Assisted mode and is a wireless device-based location determination method that uses a time difference of arrival technique to determine location. To determine location, the wireless device takes measurements of signals from nearby cellular base stations and reports the time/distance readings back to the network, which are then used to triangulate an approximate location of the wireless device. In general, at least three surrounding base stations are needed to obtain an optimal AFLT location fix. However, terrestrial-based methods tend to be less accurate than satellite-based location fixes.
As previously noted, satellite-based location determination methods generally require information from at least three satellites. Thus, the wireless device must be located in an area capable of receiving information from multiple satellites. Indoor locations, dense urban areas, and certain natural structures, like canyons and the like, may pose resistance to accurate and time efficient satellite fixes. In addition, other limitations such as erratic ionospheric conditions, noise at the wireless device level and the like may prohibit obtaining a satellite-based fix or impact the accuracy of the satellite-based fix. In these instances, it may be desirable to rely on terrestrial-based measurements to provide a less accurate, lower quality location determination.
In the same regard, certain wireless device applications that require location information may be more concerned with the speed in which a location determination fix occurs as opposed to the accuracy of the location fix. For example, in the mobile environment, applications that track the occurrence of a call event, such as a call drop, a call failure or the like, may be more concerned with determining the location at the moment the call event occurs as opposed to determining a more accurate location at a point in time removed from the call event. This is especially evident in the scenario in which the call event occurs in a moving vehicle; the call event tracking application desires an immediate location determination fix, regardless of accuracy, to be able to associate location with the call event. If the call event tracking application has to wait a certain amount of time for the location determination fix, the resulting location may be a significant distance from the location at which the call event occurred, depending on the speed of the vehicle. In this instance, the application may place a higher priority on speed at which a location is determined as opposed to the precise accuracy of the determined location.
Unfortunately, there are other problems associated with the use of GPS and other position location information by the wireless device that have not been addressed. Each time a wireless device requests and retrieves position location information, the request and retrieval processing consumes a relatively large amount of wireless device power. Further, if the wireless device does not support simultaneous voice and data calls, then the device will not be able to get a location fix during a voice call, or make a voice call during retrieval of a location fix. Also, the period of time from when the wireless device makes a requests for position fix information to when the wireless device receives the position fix information may be significant, depending on such factors as the relative position of the wireless device to the location of the satellite, the speed at which the wireless device is traveling, the performance of the position location processing system of the wireless device, the type of location determination system employed (for example, GPS, Assisted GPS, or other location determination system), and the performance characteristics of the wireless device antenna. Such parameters may exacerbate the ability of the wireless device to accurately determine the geographical position of the wireless device without draining wireless device power sources. The foregoing is particularly troubling when it is important to determine the position of the wireless device upon the occurrence of wireless device operational events, such as a call drop event on a cellular telephone.